With the continuous development of construction industry and science and technology, concretes become increasingly widely used, and thus increasingly higher requirements are imposed on the technical performance of the concretes. In practice, use of additives is confirmed to be a major way to advance the concrete technology, because with them, the concrete is adapted to meet various construction requirements, and has the advantages of low investment, quick action, convenient generalization for use, notable technical and economical benefits, and others. Superplasticizer is one of the most important concrete additives.
In recent years, high performance and pollution free are development tendency in research and production of concretesuperplasticizers. For example, maleic anhydride-based and acrylic high-performance concretesuperplasticizers are widely used in hydraulic and road engineering requiring durable concretes in America, Japan, Italia and other countries. Although the technology is mature, the process is complex and the reaction condition is harsh, which are unfavorable for generalization.
The research on high-performance superplasticizer has progressed to the 3rd generation of polycarboxylate superplasticizers, which are further subdivided into four classes, that is, copolymers of vinyl monomers, propylene oxide copolymers, polyamide/polyimide type copolymers, and amphoteric vinyl polymers. The amphoteric vinyl polymer superplasticizer is a class of highly effective superplasticizer which exhibits the highest performance in the 3rd generation of high-potent superplasticizers.
Betaine-type amphoteric monomers are a class of functional monomers that are widely used hitherto, which generally have a polymerizable alkenyl moiety and a betaine pendant moiety with electrically neutral amphoteric feature in their structure, and are of a carboxylic betaine type and a sulfonic betaine type. Amphoteric polymers having a net charge of 0 and anti-polyelectrolyte solution behaviors may be obtained from homopolymerization or copolymerization of these betaine-type amphoteric monomers alone or with other neutral monomers under certain conditions. These amphoteric polymers arouse great interest due to the high chemical and thermal stability, high hydration capacity, and the inclusion of equal number of quaternary ammonium cations and sulfonate anions that are insusceptible to the pH of the solution.
Patents CN101538352A, CN102627744B, and CN102443177B successively disclose a method for preparing an amphoteric polymeric superplasticizer, mainly through copolymerization of two cationic monomers. However, the process is complex. At present, there is no amphoteric polycarboxylate superplasticizer based on betaine monomers disclosed.